An organotypic model of oral mucosa cells for the biological assessment of 3D-printed resins for interim restorations.

STATEMENT OF PROBLEM: Three-dimensionally (3D) printed resins have become popular as a new class of materials for making interim restorations. However, little is known about how the fabrication parameters can influence biological compatibility with oral tissues. PURPOSE: The purpose of this in vitro study was to evaluate the effect of the postpolymerization time on the cytotoxicity of resins for printing interim restorations by using a 3D organotypic model of the oral mucosa. MATERIAL AND METHODS: Cylindrical specimens were prepared with conventional acrylic resin (AR), computer-aided design and computer-aided manufacture (CAD-CAM) resin (CC), composite resin (CR), and 2 resins for 3D printing (3DP) marketed as being biocompatible. The 3DPs were submitted to postpolymerization in an ultraviolet (UV) light chamber for 1, 10, or 20 minutes (90 W, 405 nm). Standard specimens of the materials were incubated for 1, 3, and 7 days in close contact with an organotypic model of keratinocytes (NOK-Si) in coculture with gingival fibroblasts (HGF) in a 3D collagen matrix, or directly with 3D HGF cultures. Then, the viability (Live/Dead n=2) and metabolism (Alamar Blue n=6) of the cells were assessed. Spectral scanning of the culture medium was performed to detect released components (n=6) and assessed statistically with ANOVA and the Tukey post hoc test (α=.05). RESULTS: Severe reduction of metabolism (>70%) and viability of keratinocytes occurred for 3DP resin postpolymerized for 1 minute in all periods of analysis in a time-dependent manner. The decrease in cell metabolism and viability was moderate for the 3D culture of HGFs in both experimental models, correlated with the intense presence of resin components in the culture medium. The resins postpolymerized for 10 and 20 minutes promoted a mild-moderate cytotoxic effect in the period of 1 day, similar to AR. However, recovery of cell viability occurred at the 7-day incubation period. The 3DP resins submitted to postpolymerization for 20 minutes showed a pattern similar to that of CR and CC at the end of the experiment. CONCLUSIONS: The cytotoxic potential of the tested 3DP resins on oral mucosa cells was influenced by postprinting processing, which seemed to have been related with the quantity of residual components leached.

Effect of thickness on shrinkage stress and bottom-to-top hardness ratio of conventional and bulk-fill composites.

This study evaluated the effect of the material thickness on shrinkage stress and bottom-to-top hardness ratio of conventional and bulk-fill composites. Six commercial composites were selected based on their different technologies: Two conventional (C1, C2), two high-viscosity bulk-fill (HVB1, HVB2), and two low-viscosity bulk-fill (LVB1, LVB2). Shrinkage stress was analyzed for five specimens with 2 mm thickness (C-factor 0.75 and volume 24 mm3 ) and five specimens with 4 mm thickness (C-factor 0.375 and volume 48 mm3 ) for 300 s in a universal testing machine. Bottom-to-top hardness ratio values were obtained from Knoop microhardness measurements in specimens with 2- and 4-mm thickness (n = 5). Thickness increase resulted in significantly higher shrinkage stress for all materials with the exception of HVB2 and LVB1. C1, C2, HVB2, and LVB1 showed lower bottom-to-top hardness ratios at 4 mm than at 2 mm. Only LVB2 presented a bottom-to-top hardness ratio lower than 80% at 2 mm, while HVB1 surpassed this threshold at 4 mm of depth. The results suggest that the increase of composite thickness affected the shrinkage stress values. Also, thickness increase resulted in lower bottom-to-top hardness ratio. HVB1 showed better behavior than other bulk-fill materials, with low stress and adequate bottom-to-top hardness ratio at 4 mm thickness.

Physical and surface properties of a 3D-printed composite resin for a digital workflow.

STATEMENT OF PROBLEM: Information related to the optical and surface properties, including health compatibility, surface roughness, and esthetics, of 3D-printed dental materials is scarce. PURPOSE: The purpose of this in vitro study was to compare the physical and surface properties of a 3D-printed resin with those of materials used for interim restorations. MATERIAL AND METHODS: A 3D-printed resin (PR) (NextDent C&B MFH; 3D Systems), an autopolymerizing interim material (BA) (Protemp 4; 3M ESPE), and a composite resin (Z350) (Filtek Z350XT; 3M ESPE) were tested for degree of color change (ΔE) (n=7) at different timepoints-24 hours after polishing/baseline (P0), 8 days after polishing (P1), and after artificial aging in water at 60 °C for 24 hours (P2)-by using a CIELab-based colorimeter; flexural strength (σ) (n=10) with a 3-point bend test; Knoop hardness (H) (n=8); and surface roughness (Ra) (n=7) with a profilometer. All specimens were polished 24 hours after polymerization, except for the additional group for surface roughness (BA) without polishing (BANP). A statistical analysis was performed by using 2-way repeated-measures ANOVA followed by the Fischer test for ΔE and 1-way ANOVA followed by the Fisher test for microhardness and surface roughness (α=.05). RESULTS: The Z350 showed the highest values for σ and H, followed by PR. BA showed the lowest results for both tests (P<.05). Considering roughness, the Z350 showed similar values to those of BA but lower than PR; PR showed similar roughness when compared with BA. PR showed the highest color variation among the groups at all timepoints, followed by BA. The Z350 was the most color stable material at all timepoints. CONCLUSIONS: The 3D-printed composite resin had adequate mechanical and surface properties for an interim restorative material. It has the potential to be a low-cost workflow in dentistry, although its color stability could be a concern for long-term use.

Management of dental caries guided by the ICDAS-LAA: a 28-month follow-up.

Dental caries is a significant oral health issue and public health concern. Currently conceptualized as a dynamic and multifactorial process, caries is a continuum of disease stages, during which tooth damage may be reversed or controlled, depending on lesion progression. The International Caries Detection and Assessment System, when used in conjunction with the Lesion Activity Assessment (ICDAS-LAA), reflects the dynamic caries process and allows the classification of cavitated lesions according to their severity and progression, which is essential to selecting the appropriate treatment. This case report describes the diagnosis and treatment of a patient who had caries in the past and in whom old lesions remained untreated. The ICDAS-LAA was used to assess caries accurately and guide treatment decisions. The patient maintained a dietary journal for 2 weeks to help establish her risk of developing caries. Treatment involved a minimally invasive dentistry approach, which consisted of remineralization via fluoride applications, placement of a composite resin restoration, microabrasion, and periodic maintenance. During the 28-month follow-up period, rigorous control of caries risk factors was achieved, and the results were satisfactory, demonstrating the effectiveness of the ICDAS-LAA in diagnosing and managing carious lesions.

A 12-month clinical trial examining the effects of a surface sealant on Class I composite resin restorations.

A split-mouth, double-blind trial evaluated the effects of a surface sealant on the clinical performance of Class I composite resin restorations. In 16 patients, 27 pairs of maxillary and mandibular molars or premolars with Class I carious lesions or unsatisfactory restorations were restored with composite resin. For each pair, 1 surface was sealed with surface sealant. Clinical evaluations of marginal integrity, marginal discoloration, anatomical form, and secondary caries were performed by 2 experienced operators using modified US Public Health Service criteria 1-2 weeks and 6 and 12 months after treatment. Data were analyzed with the McNemar test (P < 0.05). After 6 months, only 1 (4%) sealed restoration presented a Bravo rating for marginal integrity. After 12 months, the Bravo ratings for marginal integrity were 2 (7%) for sealed restorations and 1 (4%) for nonsealed restorations. Restorations received a score of Alfa for all other parameters at all time periods. There were no statistically significant differences within or between the sealed and nonsealed groups (P = 1.0). The use of a surface sealant did not improve the clinical performance of posterior composite resin Class I restorations.

Fracture strength of the remaining dental structure after different cavity preparation designs.

The aim of this in vitro study was to evaluate the loss of tooth structure after cavity preparation for direct (retentive) and indirect (nonretentive) restorations and its relationship to the fracture strength of the prepared tooth. Sound human third molars (60 maxillary and 60 mandibular) were randomly assigned into 12 groups (n = 10) according to the type of cavity preparation and the respective buccolingual width. Class II mesio-occlusodistal cavity preparations, for both indirect inlay and direct resin restorations, were prepared with standardized dimensions of one-half, one-third, or one-quarter of the occlusal intercuspal distance. Fracture resistance was lower and weight loss was greater for all nonretentive preparations. Greater losses in weight and fracture resistance occurred when the buccolingual width for both types of cavities increased, except for the weight loss of the one-quarter and one-third indirect cavity preparations in the mandibular molars, and the fracture resistance of the one-half and one-third direct cavity preparations in maxillary molars. Higher tooth structure loss and lower fracture strength were recorded after preparation of the inlay cavities.

Direct Composite Restorations to Mask Intrinsic Staining: An Eighteen-Year Follow-Up.

In this case example, the use of direct composite resin allowed for a relatively simple, conservative treatment that provided excellent function and aesthetics, while preserving healthy dental tissue. The importance of continued follow-up and a periodic maintenance and minor repair process will ensure longevity of the restorations, as aesthetics, and the occlusion.

Wear and surface roughness of silorane composites after pH cycling and toothbrushing abrasion.

PURPOSE: To evaluate the effects of toothbrushing abrasion associated with pH cycling on the surface roughness and wear of methacrylate- and silorane-based resin composites. METHODS: Microhybrid methacrylate-based (Filtek Z250), nanofilled methacrylate-based (Filtek Supreme Ultra) and microhybrid silorane-based (Filtek LS) composites were selected for this investigation. For each composite, two groups (n = 10) of rectangular specimens were made. The initial roughness (Ra) of all of the groups was evaluated based on the average of three random tracings with a profilometer, and each specimen had half of its surface protected with two layers of nail varnish to serve as controls. Half of the specimens of each resin were submitted to pH cycling, while the other half were stored in deionized water for 14 days. Subsequently, 100,000 strokes of simulated toothbrushing were performed. Final roughness and wear were measured with the same profilometer, and the values were submitted to ANOVA, Student's t-test and Tukey's test (P < 0.05). RESULTS: The data revealed an increase in surface roughness for Filtek Z250 and Filtek Supreme Ultra after toothbrushing, while Filtek LS showed the opposite behavior. Methacrylate-based composites presented lower wear values [Z250 (4.19 ± 1.73 µm); Supreme Ultra (4.16 ± 0.95 µm)], while the silorane-based composite presented increased surface roughness (11.51 ± 5.69 µm), particularly when submitted to pH cycling (15.31 ± 5.41 µm). Despite the good properties of silorane-based composites, particularly its smooth surface roughness even after pH cycling and toothbrushing abrasion, this composite still presented increased wear, which is an important issue for the development of new resin compositions.

Analysis of color stability and degree of conversion of different types of resin composites.

Resin composites containing surface pre-reacted glass (S-PRG) have been introduced to reduce demineralization and improve remineralization of the tooth structure. However, water diffusion within the material is necessary for its action, which can impair its overall physicomechanical properties over time, including color stability. This study aimed to evaluate the color stability and related degree of conversion (DC) of four resin composites. Discs (6 x 4 mm, n = 5/group) of microhybrid (MH), nanofilled (NF), nanohybrid (NH), and S-PRG-based nanohybrid (S-PRG-NH) composites with two opacities (A2/A2E and A2O/A2D) were prepared. Color (CIELab and CIEDE2000) was evaluated with a spectrophotometer after aging in grape juice (2 x 10 min/10mL/7days). The DC was analyzed by using Fourier transform infrared spectroscopy before and after light-curing. Data were statistically analyzed by using two-way analysis of variance and post-hoc least significant difference tests (p<0.05). In the color stability analysis, the interaction between filler type and opacity was significant (CIELab, p = 0.0015; CIEDE2000, p = 0.0026). NH presented the highest color stability, which did not differ from that of MH. The greatest color alteration was observed for S-PRG-NH. S-PRG fillers also influenced DC (p < 0.05). The nanohybrid resin composite presented favorable overall performance, which is likely related to its more stable organic content. Notwithstanding the benefits of using S-PRG-based nanohybrid resins, mostly in aesthetic procedures, professionals should consider the susceptibility of such resins to color alteration, probably due to the water-based bioactive mechanism of action.

The effect of baking soda when applied to bleached enamel prior to restorative treatment.

This in vitro study evaluated the effect of 10% baking soda solution and sodium bicarbonate powder (applied with jets) when applied to bleached enamel prior to restorative treatment. The surfaces of 40 bovine incisors were flattened and divided into 5 groups (n = 8): Group B (bleached and restored, negative control), Group W (bleached, stored in distilled water for 7 days, and restored), Group BSJ (bleached, abraded with baking soda jet for 1 min, and restored), Group BSS (bleached, application of 10% baking soda solution for 5 min, and restored), and Group R (restored, without bleaching, positive control). The samples were bleached in 1 session with 3 applications of 35% HP-based gel and activated with a LED appliance for 9 min each. Resin composite cylinders (2 mm height and 0.8 mm diameter) were made on the enamel surface after the acid etching and a conventional 1-step single vial adhesive application was performed. After storage in distilled water (37 ± 1°C, 24 hr), the microshear bond test was performed (1 mm/min). ANOVA and Tukey tests were applied to compare the results. The mean results of these tests showed that Groups W, BBS, and R were not statistically different. These groups also indicated a higher bond strength when compared with Groups B and BSJ. The application of 10% baking soda solution for 5 min may be an alternative pre-restorative treatment for bleached enamel, but further studies are needed to consider whether or not this treatment may be effectively used in clinical practice.

Evaluation of contact angle and mechanical properties of resin monomers filled with graphene oxide nanofibers.

This in vitro study synthesized hybrid nanofibers embedded in graphene oxide (GO) and incorporated them into experimental resin composite monomers to evaluate their physical-mechanical properties. Inorganic-organic hybrid nanofibers were produced with precursor solutions of 1% wt. GO-filled Poly (d,l-lactide, PLA) fibers and scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) characterized the morphology and chemical composition of the spun fibers. Resin composite monomers were developed and a total of 5% nanofibers were incorporated into the experimental materials. Three groups were developed: G1 (control resin monomers), G2 (resin monomers/PLA nanofibers), and G3 (resin monomers/inorganic-organic hybrid nanofibers). Contact angle (n=3), flexural strength (n=22), elastic modulus (n=22), and Knoop hardness (n=6) were evaluated. The mean of the three indentations was obtained for each sample. The normality of data was assessed by QQ Plot with simulated envelopes and analyzed by Welch's method (p<0.05). Overall, SEM images showed the regular shape of nanofibers but were non-aligned. Compositional analysis from EDS (n=6) revealed the presence of carbon and oxygen (present in GO composition) and Si from the functionalization process. The results of contact angle (°) and hardness (Kg/mm2) for each group were as follow, respectively: G1 (59.65±2.90; 37.48±1.86a), G2 (67.99±3.93; 50.56±1.03b) and G3 (62.52±7.40; 67.83±1.01c). The group G3 showed the highest Knoop hardness values (67.83 kg/mm2), and the flexural strength of all groups was adversely affected. The experimental resin composite composed of hybrid nanofibers with GO presented increased hardness values and hydrophilic behavior.

Effect of nanofibers as reinforcement on resin-based dental materials: A systematic review of in vitro studies.

This systematic review provides an update on the effect of nanofibers as reinforcement on resin-based dental materials. A bibliographic search was conducted in MEDLINEPubMed, Embase, Web of Science, Scopus, BVS (LILACS, BBO e IBECS), Cochrane, LIVIVO, and gray literature (BDTD) to identify relevant articles up to May 2021. In vitro studies that evaluated and compared the mechanical properties of nanofibers resin-based composite materials, were eligible. No publication year or language restriction was applied, and methodological quality was assessed using two methods. In a total of 6100 potentially eligible studies, 81 were selected for full-text analysis and 35 were included for qualitative analysis. Of the 35 included studies, a total of 29 studies evaluated the flexural strength (FS) of the materials. These groups were distinguished according to the resin-based materials tested and nanofiber types. Most of the studies evaluated materials composed of glass fibers and demonstrated higher values of FS when compared to resin-based materials without nanofibers. The incorporation of nanofibers into resin-based dental materials improved the mechanical properties compared to resin-based materials without nanofibers, suggesting better performance of these materials in high-stressbearing application areas. Further clinical studies are required to confirm the efficacy of resin-based materials with nanofibers.

Effect of simulated brushing on surface roughness and wear of bis-acryl-based materials submitted to different polishing protocols.

BACKGROUND: Provisional materials must have enough strength to withstand masticatory loads without suffering deformation or fracture, and their surfaces must have good finishing and polishing characteristics to reduce biofilm accumulation. Thus, the purpose of this study was to investigate the best polishing protocol for different bis-acryl composite resins in comparison with a conventional resin composite and a self-curing acrylic resin aiming to obtain a smooth restoration surface and resistance to wear. MATERIAL AND METHODS: One hundred and four samples (15 mm length x 5 mm width x 4 mm depth) were prepared and divided into four groups according to the material tested: Protemp 4 and Structur 3 bis-acryl composite resins, Dencor self-curing acrylic resin, Filtek Z350XT conventional composite resin. The polishing procedures were performed with Sof-Lex Pop-On discs or Sof-Lex spirals and abrasion procedures were performed on a brushing machine. The surface roughness was analyzed at three periods (initial, post-polishing and post-brushing) and the wear was evaluated after simulated brushing. The results were submitted to ANOVA followed by the Tukey (α = 0.05). RESULTS: Filtek Z350XT groups showed the lowest values of initial surface roughness followed by Structur 3, Protemp 4 and Dencor groups. After polishing and simulated brushing, Filtek Z350XT groups also presented the lowest roughness values, followed by bis-acryl groups (Structur 3 and Protemp 4) and Dencor groups demonstrated the highest surface roughness. Sof-Lex Pop-On discs system exhibited lower roughness values for all groups. CONCLUSIONS: Sof-Lex Pop-On discs system promoted the best polishing for all groups. Overall, Filtek Z350XT groups presented lower results for both roughness and wear for all periods evaluated, followed by Protemp 4 and Structur 3, meanwhile Dencor groups presented the highest roughness and wear values for all periods. Key words:Acrylic resin, bis-acryl, brushing, composite resin, polishing, roughness, wear.

Effects of hybrid inorganic-organic nanofibers on the properties of enamel resin infiltrants - An in vitro study.

This in vitro study aimed to evaluate the overall mechanical properties of resin infiltrants doped with bioactive nanofibers and their ability in inhibiting enamel demineralization or achieving remineralization of the adjacent enamel to white spots. A commercial resin infiltrant (ICON, DMG) was doped with hybrid inorganic-organic nanofibers and analyzed for degree of conversion (DC, n = 3) and surface hardness (SH, n = 6). Subsequently, enamel specimens (6 × 4 × 2 mm3) were prepared and submitted to a demineralizing/remineralizing process to produce a subsurface caries-like lesion. The specimens were treated with one of the following materials: ICON infiltrant, DMG (control); ICON + nanofibers of poly-lactic acid (PLA)-filled with silica (PLA-SiO2); ICON + nanofibers of (PLA)-filled with calcium incorporated into a silica network (SiO2-CaP). Then, the specimens were subjected to a pH-cycling demineralizing/remineralizing model for 7 days at 37 °C. The %ΔSH change (after treatment), %SH loss and %SH recovery (after pH-cycling regimen) were calculated after SH evaluation (n = 9/group). The Ca/P weight ratio before and after pH-cycling regimen was evaluated through SEM/EDX. The results of DC were analyzed through the T-test (p < 0.05). ANOVA followed by Tukey's test (p < 0.05) was performed for hardness and EDX. A significant SH increase was observed in the ICON/SiO2CaP group (p < 0.05). The ICON/PLA-SiO2 presented higher DC values than the control group (p = 0.043). All groups presented significant difference in %ΔSH (p < 0.05), although the specimens treated with ICON/SiO2CaP presented greater values. Regarding the %SHL and %SHR, the ICON/SiO2CaP and ICON/PLA-SiO2 were significantly different compared to the control group (p < 0.001). However, no difference was observed between the ICON/SiO2CaP and ICON/PLA-SiO2. The Ca/P ratio showed that the ICON/SiO2CaP and ICON/PLA-SiO2 after the pH-cycling regimen differed from sound enamel and modified infiltrants before pH-cycling. In conclusion, tailored hybrid nanofibers may be incorporated into enamel resin infiltrants without compromise the mechanical properties of such experimental materials. These latter can inhibit the demineralization of enamel and increase its hardness during pH-clycling challange.

Enhancing the mechanical properties and providing bioactive potential for graphene oxide/montmorillonite hybrid dental resin composites.

This in vitro study synthetized hybrid composite nanoparticles of graphene oxide (GO) and montmorillonite MMt (GO-MMt) by ultrasound treatments. Samples were characterized by X-ray diffraction, FT-Raman, FTIR, TEM and SEM. The effect of their incorporation (0.3% and 0.5%) on the mechanical properties in a resin-based composite (RBC) and their bioactivity potential were evaluated. The specimens were characterized by evaluating their 3-point flexural strength (n = 6), modulus of elasticity (n = 6), degree of conversion (n = 6), microhardness (n = 6), contact angle (n = 3) and SEM analysis (n = 3). In vitro test in SBF were conducted in the RBCs modified by the hybrid. Overall, the synthetized hybrid composite demonstrated that GO was intercalated with MMt, showing a more stable compound. ANOVA and Tukey test showed that RBC + 0.3% GO-MMt demonstrated superior values of flexural strength, followed by RBC + 0.5% GO-MMt (p < 0.05) and both materials showed higher values of microhardness. All groups presented a contact angle below 90°, characterizing hydrophilic materials. RBCs modified by the hybrid showed Ca and P deposition after 14 days in SBF. In conclusion, RBCs composed by the hybrid showed promising results in terms of mechanical properties and bioactive potential, extending the application of GO in dental materials.

Yttria-stabilized tetragonal zirconia polycrystal/resin luting agent bond strength: Influence of Titanium dioxide nanotubes addition in both materials.

PURPOSE: To evaluate the shear bond strength (SBS) between Y-TZP and a resin luting agent, after 1 of 2 enhancing strategies with TiO2--nts was applied, either to the resin luting agent or the Y-TZP mass, in different concentrations. METHODS: In the Strategy TiO2-nts on ceramic, the resin luting agent Panavia F2.0™ (Kuraray) and an experimental Y-TZP with added concentrations of TiO2--nts (0%, 1%, 2%, and 5% vol/vol) and a commercial Y-TZP, comprised 5 different groups (n = 10). In the Strategy TiO2-nts on cement, the resin luting agent RelyX U200™ (3 M ESPE) was added with different concentrations of TiO2--nts (0%, 0.3%, 0.6%, 0.9% wt/wt) luted to a commercial Y-TZP, comprising 4 different groups (n = 10). The Y-TZP discs were included in acrylic bases, and a cylinder (3 × 3 mm) of the correspondent luting agent for each respective group was applied over them. After 24 h, specimens were subjected to SBS assessments in a universal testing machine. Field emission scanning electron microscopy and energy dispersive X-ray spectroscopy analyses were also performed on Y-TZP surfaces. Data were analyzed via analysis of variance and Tukey tests (α = 0.05). RESULTS: TiO2-nts on ceramic influenced the bond strength significantly, but not linearly; TiO2-nts on cement did not influence bond strength when analyzed separately, nor in comparison with the first. CONCLUSION: Y-TZP enhancements with TiO2-nts led to a higher SBS with Panavia F2.0, a 5% TiO2--nt concentration presented the highest bond strength. Modified Rely X U200 did not improve SBS.

Polymerization shrinkage, microhardness and depth of cure of bulk fill resin composites.

The present in vitro study assessed the polymerization shrinkage/PS, Knoop microhardness/KHN and depth of cure/DC of 9 different resin composites : Filtek Bulk Fill Flowable (FBF), Surefill SDR flow (SDR), Xtra Base (XB), Filtek Z350XT Flowable (Z3F), Filtek Bulk Fill Posterior (FBP), Xtra Fill (SF), Tetric Evo Ceram Bulk Fill (TBF), Admira Fusion Xtra (ADM), and Filtek Z350XT (Z3XT). PS was assessed with a µ-CT machine, scanning 64 mm3 samples (n=8) before and after 20 s curing. KHN and DC were performed with a microhardness tester (n=8 for each group) right after 20 s light curing, with 3 readings per depth at every 0.5 mm. Low viscosity resin composites showed lower KHN values when compared with high viscosity resins. Z3XT showed the highest microhardness among the tested resin composites. Z3XT and Z3F showed lower DC when compared with bulk fill resin composites. All bulk fill resin composites presented depth of cure higher than 4.5 mm and similar or lower PS than conventional resin composites.

Shrinkage stress and elastic modulus assessment of bulk-fill composites.

Bulk-fill composites were introduced in dentistry to accelerate clinical procedures while providing adequate outcomes. Concerns regarding the use of bigger composite increments rely on the polymerization shrinkage and shrinkage stress, which may generate gaps on the adhesive interface and result in a reduced success rate. OBJECTIVE: To evaluate the polymerization shrinkage stress of different bulk-fill resin composites and their elastic modulus. MATERIALS AND METHODS: Fourteen specimens were made for each of the nine different resin composites (seven with 12 mm3 and seven with 24 mm3): Surefill SDR flow (SDR), X-tra Base (XB), Filtek Bulk Fill Flowable (FBF), Filtek Z350XT Flow (Z3F); Tetric Evo Ceram Bulk Fill (TBF), X-tra Fil (XF), Filtek Bulk Fill (FBP), Admira Xtra Fusion (ADM) and Filtek Z350 XT (Z3XT). Linear shrinkage stress was evaluated for 300 s with the aid of a linear shrinkage device adapted to a Universal Testing Machine. For each composite group, seven additional specimens (2x2x25 mm) were made and Young's modulus was evaluated with a 3-point bending device adapted in a Universal Testing Machine with 0.5 mm/min crosshead speed and 50 KgF loading cell. RESULTS: For 12 mm3 specimens, three-way ANOVA showed that only SDR and TBF generated lower stress after 20 s. Considering 300 s, TBF, SDR, and XF generated the lowest stress, followed by ADM, FBP, XB, and FBF, which were similar to Z3XT. Z3F generated the highest stress values for all time points. Considering 24 mm3 specimens after 20 s, all bulk fill composites generated lower stress than Z3XT, except XB. After 300 s, SDR, FBP, and ADM generated the lowest stress, followed by TBF and XF. For elastic modulus, one-way ANOVA showed that FBF, SDR, Z3F, and ADM presented the lowest values, followed by XB and TBF. FBP, Z3XT, and XF presented the highest elastic modulus among the evaluated composites. CONCLUSIONS: Bulk-fill resin composites presented equal to lower shrinkage stress generation when compared to conventional composites, especially when bigger increments were evaluated. Bulk-fill composites showed a wide range of elastic modulus values, but usually similar to "regular" composites.

Assessment of a conservative approach for restoration of extensively destroyed posterior teeth.

OBJECTIVE: Extensive restorations in posterior teeth always bring doubts to the clinicians regarding the best protocol, mainly when structures of reinforcement were lost. OBJECTIVE: This study aimed to evaluate the effect of beveling on the fracture resistance and pattern of class II (MOD) restored teeth. METHODOLOGY: Ninety human premolars were randomly assigned into 9 groups: CTR (control/sound); NC (cavity preparation, non-restored); RU (restored, unbeveled); RTB (restored, entire angle beveling); RPB (restored, partial/occlusal beveling); EC (endodontic access/EA, non-restored); EU (EA, unbeveled); ETB (EA, entire angle beveling); EPB (EA, partial/occlusal beveling). Teeth were restored with Esthet X resin composite and stored in distilled water for 24 h before the inclusion in PVC cylinders. The axial loading tests were performed with 500 kgF at 0.5 mm/min crosshead speed until fracture of the specimens. Fracture resistance and pattern were accessed and data were analyzed using one-way ANOVA and Tukey's HSD test (α=0.05). RESULTS: Mean (±SD) failure loads ranged from 136.56 (11.62) to 174.04 (43.5) kgF in the groups tested without endodontic access. For endodontically accessed teeth, fracture resistance ranged from 95.54 (13.05) to 126.51 (19.88) kgF. Beveling of the cavosurface angle promoted the highest fracture resistance values (p<0.05) and prevented catastrophic fractures. CONCLUSIONS: Cavosurface angle beveling is capable of improving fracture resistance and pattern for both endodonticaly accessed and non-accessed teeth.

Current Applications of Biopolymer-based Scaffolds and Nanofibers as Drug Delivery Systems.

BACKGROUND: The high surface-to-volume ratio of polymeric nanofibers makes them an effective vehicle for the release of bioactive molecules and compounds such as growth factors, drugs, herbal extracts and gene sequences. Synthetic polymers are commonly used as sensors, reinforcements and energy storage, whereas natural polymers are more prone to mimicking an extracellular matrix. Natural polymers are a renewable resource and classified as an environmentally friendly material, which might be used in different techniques to produce nanofibers for biomedical applications such as tissue engineering, implantable medical devices, antimicrobial barriers and wound dressings, among others. This review sheds some light on the advantages of natural over synthetic polymeric materials for nanofiber production. Also, the most important techniques employed to produce natural nanofibers are presented. Moreover, some pieces of evidence regarding toxicology and cell-interactions using natural nanofibers are discussed. Clearly, the potential extrapolation of such laboratory results into human health application should be addressed cautiously.